Upgrading the octane value of naphtha employing a crystalline aluminosilicate zeolite which has a high silica to alumina ratio wherein alumina is incorporated in the interstices of the zeolite crystal

ABSTRACT

Treatment and conversion of low octane, low aromatics content naphthas to both a substantially higher octane C5 to 400*F fraction and a saturated LPG (C3 + C4 stream) product by relatively low temperature contact of such naphthas with a particular zeolite catalyst material in the absence of added hydrogen. The special catalyst comprises a zeolite having shape selectivity for monomethyl substituted paraffinic hydrocarbons, which has a high silica to alumina ratio of at least about 12, a constraint index of about 1 to 12, and a crystal density not substantially below about 1.6 grams per cubic centimeter and which, by reason of its composition, is eminently well suited to the upgrading of naphtha boiling range fractions by increasing the aromatics content thereof. This zeolite may have modifying metals, such as zinc, cadmium, etc., incorporated therewith in order to improve the aromatization activity thereof. The instant improvement comprises providing aluminum, out of the crystal latice of the zeolite, e.g., by exchange or impregnation and in addition to any which may be present in a matrixing component, along with the zeolite. It has been found that such aluminum significantly decreases the proportion of dry gas, C1 + C2, produced by this process.

States Patent 1191 Morrison Mar. 18, 1975 CRYSTAL [75] Inventor: RogerA. Morrison, West Deptford,

[731 Assignee: Mobil Oil Corporation, New York,

[22] Filed: Mar. 29, 1974 [2]] App]. No.: 456,104

52] US. Cl 208/135, 260/6735, 252/4552 Int. Cl. Cl0g 35/06 Field ofSearch 260/673, 673.5; 208/135 [56] References Cited UNITED STATESPATENTS 2.971.903 2/1961 Kimberlin, Jr. et a] 208/l19 3.247.098 4/1966Kimberlin, .lr. CI al 208/135 3,702,886 11/1972 Argauer Ct ill 423/3283709979 1/1973 Chu 208/111 3,756,942 9/1973 Cattanach 208/137 37600249/1973 CZIIILmHCh 260/673 3.767.568 10/1973 Chen 208/134 3.775.30111/1973 Kaeding Cl 61 260/673 Primary E.raniiner-Delbert E. GantzAssistant ExaminerJuanita M. Nelson Attorney, Agent, or FirmCharles A.Huggett; Michael G. Gilman [57] ABSTRACT Treatment and conversion of lowoctane, low aromatics content naphthas to both a substantially higheroctane C to 400F fraction and a saturated LPG (C C stream) product byrelatively low temperature contact of Such naphthas with a particularzeolite catalyst material in the absence of added hydrogen. The specialcatalyst comprises a zeolite having shape selectivity for monomethylsubstituted paraffinic hydrocarbons, which has a high silica to aluminaratio of at least about 12, a constraint index of about 1 to 12, and acrystal density not substantially below about 1.6 grams per cubiccentimeter and which, by reason of its composition, is eminently wellsuited to the upgrading of naphtha boiling range fractions by increasingthe aromatics content thereof. This zeolite may have modifying metals,such as zinc, cadmium, etc., incorporated therewith in order to improvethe aromatization activity thereof.

The instant improvement comprises providing aluminum, out of the crystallatice of the zeolite, e.g., by exchange or impregnation and in additionto any which may be present in a matrixing component, along with thezeolite. It has been found that such aluminum significantly decreasesthe proportion of dry gas, C C produced by this process.

7 Claims, No Drawings UPGRADING THE OCTANE VALUE OF NAPHTHA EMPLOYING ACRYSTALLINE ALUMINOSILICATE ZEOLITE WHICH HAS A HIGH SILICA TO ALUMINARATIO WHEREIN ALUMINA IS INCORPORATED IN THE INTERSTICES OF THE ZEOLITECRYSTAL This invention relates to hydrocarbon conversion. It moreparticularly refers to a unique process for upgrading a low octanenaptha to a product comprising much higher octane gasoline and goodquality liquitiable petroleum gas (LPG), e.g., a saturated C +C streamand a minimum of dry gas.

As used herein, the term low octane naphtha is intended to mean apetroleum cut having a boiling range within about C to 400F whichcontains less than about 30 volume percent aromatics and has a clearresearch octane number of up to about 65. This feed is usually a virginstraight run naphtha but other low octane naphtha boiling rangepetroleum fractions, such as for example, Udex raftinate, are suitable.

Octane upgrading of virgin naphthas by means of reforming with aplatinum-alumina type catalyst is well recognized and widely practicedin the petroleum industry. This process predominantly dehydrogenates andisomerizes naphthenes to aromatics, isomerizes paraffins anddehydrocyclizes paraffins to aromatics. lt is also known to improve thequality of reformates by subjecting them to shape selective crackingusing a small pored zeolite in order to delete the remaining low octanenormal paraffins from the reformate and therefore increase the octanenumber thereof at a small yield loss. Suitable catalyst for this processare erionite type zeolites and ZSM-S type zeolites. Hydrogen is presentduring shape selective upgrading.

lt is known to directly subject virgin naphtha to hydrocracking using ashape selective hydrocracking catalyst such as nickel ZSM-S in thepresence of added hydrogen in order to upgrade the naphtha to a higheroctane hydrocrackate. This process is carried out at about 600 to 700Fand produces rather low yields (e.g., about 30 percent) of higher octanegasoline and large yields of LPG.

A recently developed process for upgrading naphtha envisions contactingthe naphtha with a ZSM-5 type zeolite at about 650 to 1500F in theabsence of added hydrogen. This process converts a substantial portionof the feed naphtha to a highly aromatic liquid product, uses hydrogengenerated by the aromatization to saturate C C gases and produces alesser proportion of LPG, and a large proportion of dry gas, that is C,and C It has been proposed to modify the catalyst used for this processin order to increase its aromatization activity by incorporating variousmetals, notably zinc or cadmium, therein by impregnation, exchange orotherwise. The process temperature is to some extent a function of thefeed composition. Olefinic feeds can be treated at about 650F and higherwhile paraffinic feeds can be treated at about 850F and higher. Goodoperations with virgin naphthas are realized at about 900 to l200F.

It is an object of this invention to provide a novel process forupgrading naphthas.

It is another object of this invention to provide a novel process forconverting'virgin naphthas to a high uct without hydrogen consumption.

Other and additional objects of this invention will become apparent froma consideration of this entire specification including the claimshereof.

In accord with and fulfilling these objects, one aspect of thisinvention resides in a process of upgrading naphtha having a lowaromatics content, and preferably a highly paraffinic naphtha, by asimultaneous aromatization and hydrocracking operation carried out atrelatively limited reaction conditions with a special catalyst.

The catalyst used in this invention is based upon a syntheticaluminosilicate zeolite which was prepared utilizing an organic cation.This zeolite is shape selective for methyl substituted paraffins andsmaller effective diameter molecules, has a silica to alumina ratio ofat least about 12, preferably at least about 35-70, and has a constraintindex of about 1 to 12, preferably about 2 to 7. The constraint index ofa particular zeolite is determined by grinding the zeolite to theconsistency of coarse sand; placing about one (1) gram thereof into aglass tube; treating the zeolite with air at 1,000F for at least 15minutes; flushing with helium while lowering the temperature to 550 from950F; replacing the helium with an equal weight mixture of nhexane and3-methyl pentane admixed with four (4) times its total moles of helium;passing this over the zeolite at a space velocity of l LHSV andatmospheric pressure for twenty (20) minutes; and sampling the effluentgas. The constraint index of the zeolite is the ratio of the logarithmof the fraction of n-hexane remaining divided by the logarithm of thefraction of 3- methyl pentane remaining. The zeolite should alsopreferably have a crystal density of not substantially below about 1.6grams per cubic centimeter.

Zeolites as described and defined herein are suitably modified in aknown manner to incorporate therewith zinc, or cadmium or othersimilarly behaving metals in order to enhance their aromatizationactivity.

Representative synthetic zeolites which conform to the above-identifiedparameters are ZSM-S, described in US. Pat. No. 3,702,886; ZSM-l ldescribed in US. Pat. No. 3,709,979; ZSM-l2, described in West GermanOffenlagunschrifft Pat. No. 2,213,109; ZSM-2l, described in US.application Ser. No. 358,192 filed May 7, 1973; and TEA mordenite,described in US. application Ser. No. 130,442, filed Apr. 11, 1971. Thecontents of these patents, applications and publication are incorporatedherein by reference.

In accord with this invention, this metal modified zeolite is furthermodified in such manner as to surprisingly surpress the conversion offeed naphtha to undesirable dry gas (C C This can be accomplished byincorporating aluminum with the zeolite. In this regard, it is to beunderstood that the aluminum referred to herein excludes aluminum in thecrystal latice of the zeolite and excludes aluminum in the form ofalumina which is part of all of a matrixing material sometimes used inconjunction with zeolite catalysts. Rather, the aluminum referred toherein and forming an important part of this invention is interstitialaluminum, that is in the interstices of the zeolite crystal. Thisaluminum is suitably intersticially incorporated with the zeolite byconventional exchange, impregnation or vapor deposition techniques, withexchanged in aluminum being preferred. It is also within the spirit andscope of this invention to provide the interstitial aluminum byextraeting such from the zeolite framework crystal by means of suitablecalcination procedures. For example, if the zeolite has a rather lowsilica to alumina ratio of about 35, calcination in a thick bed seems toprovide a greater tendency for the crystal latice to be dealuminized tosome extent and at least part of the aluminum thus freed to depositinterstitially and thereby affect the dry gas make in the instantprocess. On the other hand, zeolites having a relatively high silica toalumina ratio of about 70 seem to dealuminize better upon calcination ina thin bed.

In any case, it is not really known or understood whether thick or thinbed calcination is better for incorporating aluminum according to thisinvention because, in addition to the silica to alumina ratio being anapparently important variable, the crystal size of the zeolite prior tocalcination seems to affect the deposition of aluminum for the crystallatice into the crystal interstices.

Suffice it to say that there are many known ways of incorporatingintersticial aluminum with a crystalline zeolite, any or all of whichappear to be pertinent to the practice of this invention.

Not only is it important to judiciously select the particular zeolite tobe used as a catalyst for the instant process, it is similarly asimportant to modify the selected zeolite by incorporating therein aneffective amount up to about weight percent zinc and/or cadmium and aneffective amount up to about 10 weight percent aluminum. Preferably atleast about 0.4 weight percent of each of aluminum and zinc or cadmiumare incorporated with the zeolite, and most preferably the incorporatedproportion of both zinc or cadmium, and aluminum is up to about 7 weightpercent. While the zinc or cadmium and aluminum can be incorporated byany known technique, such as for example, impregnation, exchange, vapordeposition or some combination thereof, it is preferred in the practiceof this invention to utilize a zeolite having both zinc or cadmium andaluminum exchanged thereinto. In regard to the addition of modifyingmetals, the zeolite catalyst, it is interesting to note that theaddition of zinc to a zeolite as described herein generally causes anincrease in aromatization activity and selectvity of the zeolite. Theaddition of aluminum alone has not previously been reported asdecreasing the aromatization activity and/or selectivity of thesezeolites, yet the mixture of zinc or cadmium and aluminum utilizedherein seems to have a synergistic effect in reducing conversion of thenaphtha charge stock to aromatics increasing the conversion of thecharge to LPG; decreasing the conversion of charge to dry gas; andproducing a liquid product having at least as high or even higherresearch octane number and octane number improvement than when carryingout an aromatization conversion using the same zeolite modified only byincorporation of zinc.

The process of this invention is to be distinguished from previouslydescribed aromatization processes using a similar zeolite catalyst inthat the operating temperature is generally lower, e.g., about 600 to750F, than would be used with a feed or comparable parafinicity and thearomatics make is lower than the minimum 30 grams per 100 grams setforth in this prior work. It is similar to such aromatization process inthat it operates at low space velocities of up to about WHSV, preferablyabout 0.75 to 5 WHSV. 1t is also similar to such aromatization in thatit neither desires nor requires the co-feeding of hydrogen with thenaphtha charge.

The process of this invention is to be distinguished from previouslydescribed hydrocracking processes using a similar zeolite catalyst inthat while such hydrocracking process utilizes a high added hydrogen tohydrocarbon ratio and requires a hydrogenation/dehydrogenation componentin the catalyst formulation, the process of this invention does notconsume hydrogen nor does it require or desire ahydrogenation/dehydrogenation catalyst component. The instant processfurther differs from the prior hydrocracking process in thathydrocracking necessarily operated at substantial superatmosphericpressure whereas in this process it is desirable to operate at low or nopressure; this process is preferably operated at about atmosphericpressure.

This invention will be illustrated by the following Examples which arenot considered to be limiting upon the scope hereof. Parts andpercentages are by weight unless expressly stated to be on anotherbasis.

EXAMPLE 1 (PRIOR ART) A C 330F Arabian straight run naphtha having aresearch octane number of 40 and a PONA analysis of:

Paraffins 63.5 WGT. 72 Olefins 0 7r Naphthenes 20.1 7! Aromatics 16.4 71

was hydrocracked over a Ni ZSM-S (0.68 percent Ni) catalyst at 660F, 650psig, 5 to 1 hydrogen to hydrocarbon ratio and a space velocity of 3WHSV. Conversion was 69.3 percent. The liquid product had a C to 400Fclear research octane of 91. The gas make (Cf) was 61.8 percent of which13.9 percent was isobutane and 1.2 percent was dry gas. The remaining46.7 percent was LPG. No new aromatics were formed.

EXAMPLE 2 (PRIOR ART) A refinery stream similar to that used in Example1, C C Udex raffinate, having a research octane of 61 and a PONAanalysis of:

Paraffins 89.9 Wgt. Olefins 0 72 Naphthenes 3.4 Aromatics 6.7 72

was aromatized over a Zn ZSM-S (7 percent Zn) catalyst at 800F, 0 psig,0 hydrogen and a space velocity of 1 WHSV. Conversion was 61.2 percent.The liquid product had a C to 400F clear research octane of 89. The gasmake was 33.2 percent of which only 7.2 percent was isobutane and 4.5percent was dry gas. LPG product accounted for 12.6 percent. Newaromatics were made at a rate of 23.4 parts per parts of charge.

EXAMPLE 3 The same refinery stream as used in Example 2 was processedaccording to this invention by passing it over an Al-Zn-ZSM-S (3percentAl and Zn) at 700F, 0 psig. 0 hydrogen and a space velocity of 1 WHSV.Conversion was 78.6 percent. The liquid product had a C to 400F clearresearch octane of 90. The gas make was 55.2 percent of which 13.9percent was isobutane. So

far the same isobutane make as in Example 1, operating according to thisinvention made substantially more gasoline of almost equivalent octanenumber. As compared with Example 2, operating according to thisinvention made somewhat less aromatics (18.3 percent) and somewhat lesshydrogen (0.25 percent vs. 0.79 percent) but made substantially more LPGand less dry gas. Since dry gas is the least valuable product producedin naphtha upgrading, a four fold reduction thereof from 45 percent ofthe product to 1.2 percent of the product makes this invention mostvaluable.

Example 3 was rerun with somewhat different modified catalyst. 1n thefollowing Examples 4 through 6, the catalyst was a zinc exchanged ZSM-Shaving a silica to alumina ratio of about 70 and a zinc content of about0.8 percent.

Table l in contact wTth an aromatization improving modified syntheticcrystalline aluminosilicate zeolite having a silica to alumina ratio ofat least about 12, a constraint index of about l to 12, and a crystaldensity of not substantially less than about 1.6 grams per cubiccentimeter; the improvement, whereby increasing the production ofsaturated C C. LPG while maintaining production of higher octanegasoline having a clear research octane number of at least about 85,which comprises contacting said naphtha with said zeolite catalysthaving aluminum incorporated into the interstices of the zeolite crystalabout 600 to 750F in the absence of added hydrogen at a space velocityof up to about 15 WHSV.

2. The improved process claimed in claim 1 wherein said zeolite isZSM-S.

In the following Examples 7-10, the catalyst was an aluminum exchangedZSM-5 having a silica to alumina ratio of about and an aluminum contentof about 0.8 percent.

3. The improved process claimed in claim 1 wherein said aluminum isincorporated in proportions of up to about 10 weight percent.

4. The improved process claimed in claim 11 including Table 2 ExampleNo. Temp F Conversion C R+O Gas Make 7: l-C C -C The following examplescompare the results obtained from practicing this process with a ZSM-5zeolite which has been respectively zinc exchanged and then thin bedcalcined (TBC), zinc exchanged and then thick bed calcined (HBC), andaluminum and zinc exchanged (E). It also notes certain differences inresults depending upon whether small(s) crystal size or large(l) crystalsize zeolite was used:

zinc in addition to aluminum both being present in 5 cumulativeproportion of about 0.5 to 7 percent by weight.

5. The improved process claimed in claim 1 wherein said catalyst isZSM-S having zinc and aluminum exchanged thereinto.

6. The improved process claimed in claim 1 wherein said modified zeolitehas a silica to alumina ratio of up Table 3 Example No. S,O /Al. O ModConversion 71 C -,*R+O Gas Make 70 C,+C

11 70 TBC-l 63.5 83.5 42.6 2.0 12 70 HBC-l 67.6 85.6 46.0 2.3 13 70 E-]72.3 86.2 53.7 1.4 14 71) TBC-s 71.3 86.1 49.6 1.7 15 70 HBC-s 72.4 85.951.6 1.9 16 70 B5 73.9 87.6 54.2 1.4 17 35 TBC-l 72.6 86.9 52.5 1.6 1835 HBC-l 74.5 88.1 56.4 1.2 19 35 E-l 77.0 89.8 56.5 1.1 211 35 TBC-S75.9 89.7 55.2 1.7 21 35 HBC-s 75.2 90.1 53.8 1.5 22 35 E-s 78.2 90.357.8 1.5

What is claimed is: to about 70.

1. In the process of upgrading the octane value of naphtha having aclear research octane number of up to about 65 by converting such atelevated temperature 7. The improved process claimed in claim 1 whereinsaid aluminum is incorporated during calcining.

1. IN THE PROCESS OF UPGRADING THE OCTANE VALUE OF NAPHTHA HAVING ACLEAR RESEARCH OCTANE NUMBER OF UP TO ABOUT 65 BY CONVERTING SUCH ATELEVATED TEMPERATURE IN CONTACT WITH AN AROMATIZATION IMPROVING MODIFIEDSYNTHETIC CRYSTALLINE ALUMINOSILICATE ZEOLITE HAVING A SILICA TO ALUMINARATIO OF AT LEAST ABOUT 12, A CONSTRAINT INDEX OF ABOUT 1 TO 12, AND ACRYSTAL DENSITY OF NOT SUBSTANTIALLY LESS THAN ABOUT 1.6 GRAMS PER CUBICCENTIMETER, THE IMPROVEMENT, WHEREBY INCREASING THE PRODUCTION OFSATURATED C3-C4 LPG WHILE MAINTAINING PRODUCTION OF HIGHER OCTANEGASOLINE HAVING A CLEAR RESEARCH OCTANE NUMBER OF AT LEAST ABOUT 85,WHICH COMPRISES CONTACTING SAID NAPHTHA WITH SAID ZEOLITE CATALYSTHAVING ALUMINUM INCORPORATED INTO THE INTERSTICES OF THE ZEOLITE CRYSTALABOUT 600* TO 750*F IN THE ABSENCE OF ADDED HYDROGEN AT A SPACE VELOCITYOF UP TO ABOUT IS WHSV.
 2. The improved process claimed in claim 1wherein said zeolite is ZSM-5.
 3. The improved process claimed in claim1 wherein said aluminum is incorporated in proportions of up to about 10weight percent.
 4. The improved process claimed in claim 1 includingzinc in addition to aluminum both being present in a cumulativeproportion of about 0.5 to 7 percent by weight.
 5. The improved processclaimed in claim 1 wherein said catalyst is ZSM-5 having zinc andaluminum exchanged thereinto.
 6. The improved process claimed in claim 1wherein said modified zeolite has a silica to alumina ratio of up toabout
 70. 7. The improved process claimed in claim 1 wherein saidaluminum is incorporated during calcining.